The present invention relates to a multi-jet generator device useful in ink jet printers, such as those used as output devices for computers and the like, for printing, marking or plotting on various surfaces.
Ink jet printers employ various physical forces to take small quantities of ink from a reservoir, convert them into droplets, and transport the droplets through the air to the printing medium, such as paper, transparencies, metal, glass etc. The forces used to create and transport the droplets may be mechanical, electrostatic or thermal. Ink jet printers fall into two main categories--continuous-jet and drop-on-demand.
In both types of devices, droplets are formed by forcing a printing fluid, or ink, through a nozzle. Hence, the ink-jet devices typically include a multitude of very small diameter nozzles. Drop-on-demand systems typically use nozzles having openings ranging from 30 to 100 .mu.m while Hertz continuous-jet systems typically use nozzles having openings ranging from only 10-20 .mu.m.
The use of such nozzles leads to a number of difficulties, not the least of which is the relatively high incidence of nozzle clogging, high cost of manufacture, the requirement for tight tolerances and strict materials limitations. To avoid nozzle clogging and increase the reliability of such printers, high-grade fine filters must be used upstream of the nozzle to avoid dirt particles in the ink from reaching the nozzle. Furthermore, during the time the printer is not in use, the ink should not dry in the nozzle since a solid deposit will also result in clogging. To avoid this difficulty a humectant is used in the ink to prevent the ink from drying except when it contacts the paper. The ink must also contain fungicides to prevent biological growth which could result in nozzle clogging by fungi or bacteria. To obtain ink of a required color, a suitable dye must be added to the ink. Color pigments cannot be used since they clog the nozzle or the filter. The choice of dye is critical since the dye must not form a solid deposit with the humectant if the ink is allowed to dry in the nozzle.
All these strict requirements relating to the inks, severely limit the choice of inks which may be used in ink-jet systems using nozzles. Much research has been devoted to optimizing ink compositions in an attempt to find inks which have suitable characteristics. Typically, an ink found to be suitable represents a number of tradeoffs and compromises with respect to a series of properties.
There is thus a widely recognized need for, and it would be highly advantageous to have, an ink jet system which does not include the fine nozzles present in conventional systems and which would, therefore, be able to operate with a wide variety of ink composition without decreasing the reliability of the system.